Metal Replacement Gains Velocity in Automotive

Think there are no more metal-to-polymer conversions left in automotive design? Think again.

Materials development efforts in the past several years that were aimed at raising stiffness, impact, and heat resistance have succeeded on all counts. Combine that with the increasing sophistication of automotive designers, who are pushing the envelope on material selection as they seek to reach fuel economy goals, and you have a perfect setting for the next generation of metal replacement.

Automotive designers were originally focused on replacing metal with plastics in a limited number of applications, but today’s polymeric materials are meeting the challenges of emerging design and engineering criteria in more areas of the vehicle.

While the easy applications have long since been converted -- those that are left are the tougher ones -- the good news is that the palette of polymer alternatives has become tougher, as well. Further, automotive engineers now have a better grasp of best-practices for designing with polymers.

Rather than looking for materials that can replace a metal part using the identical geometry, designers are now capitalizing on the additional freedom to form plastics into net shapes. The substitutions aren’t limited to metal either. Designers are also replacing thermoplastic vulcanizates (TPVs) with easily recyclable and colorable thermoplastic elastomers for a host of benefits. Let’s take a look at some reasons and examples.

Automotive HVAC units that switch from TPVs to TPEs not only perform better, but can be manufactured more efficiently.

Reducing weight is at the top of the list. Studies by the EPA and other organizations show that every 5 percent of vehicle weight removed can improve fuel economy by 2 percent. Generally, replacing a metal component with a plastic one results in a 50 percent weight reduction, so the math is attractive to designers striving to reach Corporate Average Fuel Economy (CAFE) targets.

Better fuel economy also means lower greenhouse gas emissions, which rose again globally by 2 percent in 2012 to a record high of 2.4 million pounds per second.

Running a close second on this list is the additional design freedom that today’s advanced plastics afford. In other words, advances in polymer formulation technology are enabling more design freedom than ever before. Rather than welding, fastening, and bending -- all of which require secondary operations and therefore more cost -- most automotive plastic parts are produced to net shape in one automated operation.

Geometry is yet another freedom. Plastic part design has become a sophisticated science, enabling parts to be designed to exact contours to save space under the hood. Additionally, bumpers and fascia can be more aerodynamic and stylish, and interior components can bend to the designer’s will for greater differentiation.

Finally, all of these factors combined allow multiple metal parts to be redesigned and replaced by plastics and consolidated into a single unit for reduced after-sale maintenance and production process improvement.

With 54.5-mpg CAFE mandates looming, most automakers are deseperate to find ways to cut weight. If suppliers can develop the mechanical strength needed for body panels and seat components, and provide the heat resistance for underhood components, automakers will snap up these materials.

The low-hanging fruit of plastic-to-metal conversion is no longer there for the taking, but that doesn't mean there are no opportunities. This article does a good job of explaining how to go about finding these opportunities: design engineers should sit down with suppliers or other experts, with a focus on part function. You are probably not going to make the same exact part out of plastic that you made out of metal -- at least, not if you want the part to work! But, with a little creativity, you might be able to get the same function. It takes design ingenuity, along with a knowledge of what's out there in terms of materials. This is where suppliers and outside experts can help.

Designing trade-offs are always more complex than getting exact matches of properties. The thermally conductive compounds referenced in the article have thermal conductivities up to about 20 W/mK. While that isn't quite equivalent to aluminum at 100W/mK, it's over 3 orders of magnitude improvement over base plastics which sit at around 0.1 W/mK.

That does make these formulations viable options for heat management. We've done several design cases in areas such as automotive lighting and have shown that those sorts of conductivities are more than enough to replace metal heat sinks which in many cases are *overspecified* for thermal conductivity.

As to 3D printing. We have 3D printing capability and development programs to be able to print some of our key functional formulations. Happy to discuss further if you like.

Not that conductive, but sounds like a great material that can both house and supply data for low voltage sensors. I wonder if this is being explored. Also, a great way to send power or a signal through a enclosed container. That is if both conductive and non-conductive plastics can be molded together. Sound like this will revolutionize the automotive sector sometime soon.

I found myself wondering if there were some polymer/metal hybrid materials out there for use in automotive applications? Is that a practical tradeoff for weight, strength, conductivity, etc.? Any thoughts?

I agree Kendall. The improved thermal conductivity of many polymers is now opening design doors that were previously closed for us. In addition to metal heat sinks that may have been overspecified in the past, new LED technologies burn cooler and brighter, so the opportunity to replace a metal heatsink with a thermally conductive plastic heatsink may now be available.

Scott, not sure what sort of construct you mean specifically by a 'hybrid.' Some of our systems are filled with various substances. Metals sometimes play a role. But the metal itself doens't play a role for strength. Obviously the trade-off when systems are more highly filled is for strength properties (flex mod, impact). I think maintaining this balance is more critical for automotive applications than say electronics. We are also looking at composite-based constructs for these types of properties. Best, Kendall -

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